User blog comment:Gyradoes/Some confusion/@comment-35002745-20180528232006/@comment-32358261-20180528233334

Because by the time anime started gen 2 was being developed I believe.

Pokémon movies usually do that and reveal new Pokémon from the next gen.

Pokémon 4ever had the Lati duo, Mystery of mew had lucario, master of illusions had zoroark and genesect and the legend awakened had mega mewtwo y